Scales can be used as a metaphor for comparing different options.
Simple scales consist of a heavy platform, above which a beam hangs freely on a stand. At the ends of the beam are two pans.
These scales allow you to determine only which pan has the heavier load. To use them to find out the weight, you need to put what needs to be weighed on one pan, and on the other - enough weights to balance the scales, after which you add up the weights of all the weights used.